This heavenly city, then, while it sojourns on earth, calls citizens out of all nations, and gathers together a society of pilgrims of all languages, not scrupling about diversities in the manners, laws, and institutions whereby earthly peace is secured and maintained, but recognizing that, however various these are, they all tend to one and the same end of earthly peace. It therefore is so far from rescinding and abolishing these diversities, that it even preserves and adopts them, so long only as no hindrance to the worship of the one supreme and true God is thus introduced. Even the heavenly city, therefore, while in its state of pilgrimage, avails itself of the peace of earth, and, so far as it can without injuring faith and godliness, desires and maintains a common agreement among men regarding the acquisition of the necessaries of life, and makes this earthly peace bear upon the peace of heaven; for this alone can be truly called and esteemed the peace of the reasonable creatures, consisting as it does in the perfectly ordered and harmonious enjoyment of God and of one another in God. When we shall have reached that peace, this mortal life shall give place to one that is eternal, and our body shall be no more this animal body which by its corruption weighs down the soul, but a spiritual body feeling no want, and in all its members subjected to the will. In its pilgrim state the heavenly city possesses this peace by faith; and by this faith it lives righteously when it refers to the attainment of that peace every good action towards God and man; for the life of the city is a social life.
Augustine, City of God, Book XIX, chapter 17